1. Field of the Invention
The present invention relates to a method of scheduling a plurality of cells in a temporal frame, and more particularly, to a method of scheduling a plurality of time division multiplex (TDM) cells in a synchronous optical network (SONET) frame.
2. Background
The telecommunications industry has developed schemes for transmitting telephony signals, which are usually in the form of time division multiplex (TDM) signals that have been formatted into asynchronous transfer mode (ATM) cells over a physical layer interface, such as a synchronous optical network (SONET) interface. The SONET uses an industry-standard framed transmission format in which signals are transmitted in SONET superframes each having a duration of 1 ms. Each SONET superframe is divided into 8 SONET frames each having a duration of 125 .mu.s. Each SONET frame includes a plurality of cells each adapted to carry data in the ATM format. Digital video signals and computer data signals are usually carried in the ATM format whereas telephony signals are usually carried in the TDM format. Systems and methods have been developed to carry both telephony and digital video signals over the same communications network. Methods have been developed to convert the TDM format into the ATM format such that both telephony and digital video signals can be transmitted over a single physical layer interface.
However, when the SONET frames are received by a SONET octal bus over a plurality of ports, address collisions may occur between cells of different SONET frames. For example, if a TDM cell in a frame overlaps with another TDM cell in an adjacent frame when received by a receive interface such as a SONET octal bus, an address collision occurs which causes jitters that are undesirable for the demultiplexing of the TDM signals. Therefore, there is a need for a method of scheduling the TDM cells in the SONET frames to avoid an address collision between the TDM cells of different frames even if the frames are received by the receive interface with some overlap.